#include<cstdio>
#include<fstream>
#include<iostream>
using namespace std;
int const maxn=1e5+10;
struct segment
{
    bool cond;
    int sz,pos;
    segment(){cond=sz=pos=0;}
    segment(bool _cond,int _sz,int _pos)
    {
        cond=_cond;
        sz=_sz;
        pos=_pos;
    }
    bool operator<(const segment &k)const
    {
        return pos<k.pos;
    }
};
int n,a_sz;
int ans_cnt=0;
char s[maxn];
//set<segment>st;
//segment a[maxn];
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    ifstream fin;
    fin.open("freddy.in");
    ofstream fout;
    fout.open("freddy.out");
	//scanf("%d",&n);
	//scanf("%s",&s);
	fin>>n;
	fin>>s;
	char last=s[0];
	int last_sz=1;
	for(int i=1;i<n;++i)
    {
        if(s[i]==last)
            last_sz++;
        else
        {
            /*a[a_sz++]=segment((last=='0')?0:1,last_sz);
            st.push(segment((last=='0')?0:1,last_sz));
            last_sz=1;*/
            if(last=='1')ans_cnt++;
            last=s[i];

        }
    }
    //printf("%d\n",ans_cnt);
    fout<<ans_cnt<<'\n';
    fin.close();
    fout.close();
    /*a[a_sz++]=segment((last=='0')?0:1,last_sz);
    segment b=a[1],c=segment(0,-1);
    for(int i=1;i<a_sz;i++)
    {
        if(a[i].cond==0)
        {
            if(b.cond==0)
                b.sz+=a[i].sz;
        }
        a[i]
    }*/
    /*int ans_cnt=0;
    st.push(segment((last=='0')?0:1,last_sz));
    auto it=st.begin();
    for(it++;it!=st.end();++it)
    {
        auto it1=it--;
        if(it1->cond<it->cond)continue;
        if(it->cond==it->cond)
        {
            it->sz+=it1->sz;
            st.erase(it1);
        }
        else///it->cond<it1->cond
        {

        }
    }*/
return 0;
}